This is a modular tunnel system that enables you to piece together tunnel schematics, allowing you to connect different areas of your world quickly and neatly. This particular set is made using Stone bricks and Soul Stone bricks. I have about 20 other varieties ready, I just haven't had time to save out the schematics. (Like cutting out and saving schematics? If so I have work available. :)
Use these as you see fit in your build. Permission is granted to modify them to fit your worlds look - if you come up with something cool, I would love to see it. Giving credit is appreciated.